Our project seeks to apply an objective behavioral measure of brain function that may identify sites of neural dysfunction in autism spectrum disorder (ASD). Our paradigm will be a robust measure of associative learning - Pavlovian eyeblink conditioning (EBC) - to assess how fundamental building-blocks of higher brain function may be disrupted in school-aged children with ASD. The subjects will be 99 10-year-old children that are currently participating in one of two longitudinal studies examining: 1) the effet of an early behavioral intervention on the cognitive development of children with ASD; and 2) the neurochemical and neurostructural risk factors for developing ASD. Of note is that all of our subjects have had neurochemical and structural imaging at 24 months of age along with ongoing longitudinal clinical and behavioral assessments up to the current time. The project builds upon strong preliminary data demonstrating that ASD severity and EBC performance deficits are related. Our goal is to apply EBC in a well-controlled group of children whose ASD history has been extensively documented to determine whether EBC can aid in understanding long-term developmental outcome. Because the children had high-resolution anatomical brain scans and neurochemical imaging at approximately 24 months of age, we can now relate variability in EBC performance to alterations in early brain morphology and metabolism. An advantage of EBC is that it does not require language, social interaction, or active participation. Thus, EBC can be applied equally to high-functioning children and very low- functioning children with ASD for whom quantitative measures of behavioral development are difficult to obtain. The project will have the following impact: 1) it will address a crucial need for long-term outcome studies of developmental processes and outcomes in ASD; 2) it will help to identify the underlying neural mechanisms of ASD; 3) it could point to implementing EBC at earlier ages to assess ASD risk.